The manufacture of fiber pulp from lignocellulose-containing material is generally carried out in a refiner comprising two grinding discs, at least one of which is rotary. This is generally accomplished in a manner such that the material is fed in through a central opening in one disc and disintegrated in the gap between the discs, while water is simultaneously being supplied thereto. Conventionally, the grinding discs are provided with raised bars and intermediate grooves, which extend from the center outwardly to the periphery of the grinding discs. Such methods for the manufacture of mechanical cellulose pulp have been known for a considerable period of time.
The pulps which are manufactured in such a conventional manner, however, generally contain a large fraction of relatively long fibers. In certain applications, such as for use as newsprint, this can be of value, primarily because it results in high strength, especially tear resistance, which is essential in view of the high machine speeds used during the manufacture and printing of same.
In other quality papers, such as magazine paper and LWC (light weight coated) paper, however, the printability of these papers is of greater importance, and the necessary strength in these cases is generally achieved by admixing chemical pulp therein.
Thermomechanical pulp (TMP) and chemi-mechanical pulp (CTMP) are pulps which are produced in very high yields, e.g., 90 to 95%. This implies that substantially all of the lignin remains in the pulp. The long fibers thus become rigid, and the smoothness of the paper is considerably deteriorated.